448 



PLAGIAULAX. 



With reference to the angular process, I have nothing to 

 add to what is set forth in niy former communication. This 

 process, which is a very constant character of the carnivoroiis 

 jaw, is wanting as a salient apophysis in Plagiaulax, although 

 well developed in the minute insectivorous Myrmecobius. 



I have one remark more to make in reference to the form of 

 Plagiaulax. Fig. 2 of PL XXXIV. gives a representation of 

 what remains of the lower jaw of P. minor, magnified to a 

 scale of four diameters. The entire length of the specimen, 

 including the six molars and premolars, together with the 

 procumbent incisor (according to the metrical line e), does 

 not exceed '4 of an inch, of which the six cheek-teeth united 

 make only about two and a half lines (*25 inch). I ask any 

 zoologist or comparative anatomist to look at it, and say 

 whether the dental apparatus of this extremely minute crea- 

 ture is competent to perform the duties required of a preda- 

 ceous carnivore. Magnitude in this case is an important in- 

 gredient, as it necessarily involves measure of force. Could 

 P. minor have preyed on small Mammals and Lizards ? Is 

 it not more probable that this pigmy form was itself an ob- 

 ject of prey in the Purbeck Faima ? 



In the preceding observations I have gone seriatim into the 

 objections raised against the view which I advanced of the 

 affinities of Plagiaulax. In the work referred to, every detail 

 of external form was regarded in a light different from that 

 in which it was viewed by me ; every inference was contro- 

 verted ; and the conclusion drawn from the whole was diame- 

 trically the converse of that arrived at by me. The verdict of 

 Comparative Anatomists will decide which is right. I have 

 reconsidered rny first inferences, and tried to test their validity 

 by the strongly contrasted and extreme view put forward by 

 Professor Owen; and the result has been to confirm the 

 opinion that Plagiaulax did not belong to a carnivorous type 

 of Marsupials. Regarded morphologically, in the plan of its 

 dental system ; rationally, through its condyle and correlated 

 characters ; and empirically, by comparison with Hypsip- 

 rymnus and Cheiromys, it has led me, through every aspect, 

 to this conclusion. Enough has been adduced in the fore- 



glenoid cavity preventing protrusion or 

 retraction of the lower jaw ; and the 

 muscular power being applied close to 

 the condyle leaves the free part of the 

 lever longer, or, in other words, admits 

 of a wider separation of the jaws in 

 front, for the canines and cutting-teeth 

 to act. In the Aye-Aye and Rodents 

 (e. g. Cavia and Hystrix) the fulcrum is 

 moveable, the condyle playing on a flat 

 glenoid surface ; the point of insertion 



of the muscular power is more advanced, 

 leaving a short portion of the lever free, 

 and thus restricting the aperture of the 

 jaws. These conditions combined with 

 the oblique direction of the temporal 

 muscle, implied by the reclining coro- 

 noid, conspire to produce the antero- 

 posterior and lateral motions required 

 by the regimen of these forms. The 

 same reasoning ajjplies to Plagiaulax. 



